Hannibal - from Pushing Daisies creator Bryan Fuller - will focus on the early days of the cannibal killer.
Black Hawk Down star Dancy will play FBI agent Will Graham, according to TVLine.
The character was previously portrayed by CSI's William Petersen in 1986 film Manhunter and by Edward Norton in 2002's Red Dragon.
Dancy currently appears on Showtime's The Big C and recently starred in film thriller Martha Marcy May Marlene.
NBC ordered 13 episodes of Hannibal last month. An actor is still being sought for the title role, with Oscar-winner Anthony Hopkins and Scottish actor Brian Cox having previously played the part.
Fuller is also developing a reboot of '60s series The Munsters at NBC. The update - titled Mockingbird Lane - recently cast actor and comedian Eddie Izzard.
> Anthony Hopkins: 'Hannibal was role of a lifetime'
Watch the trailer for 2002's Red Dragon - starring Edward Norton as Will Graham - below: